In the Invention in F major BWV 779 by J. S Bach, several seventh chords (C, B, A) in the left hand descend in seconds. Dividing each seventh chord into two triads, we realize that the chords are the result of a hidden sequence of fourths (G - C - F - F - B - E - A):

This sequence is a variant of the sequence of fourths and fifths. Two chords of each fourth interval combine to form seventh chords:

Another example

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This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. José Rodríguez Alvira.
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